Method accounting for thermal effects of lighting and radiation sources for spectroscopic applications

ABSTRACT

A method of spectral measurement utilizing sensing devices that employ light or radiation sources. The method provides a uniform spectra or wavelength intensity reading with respect to the temperature or intensity by using an algorithm that incorporates the thermal aspects of the light or radiation source with the spectral, sensing or color attributes.

FIELD OF THE INVENTION

This invention is in the field of spectral measurements or other sensingdevices that employ lighting and radiation sources. In particular, thepresent invention relates to providing a more uniform and accuratespectra or wavelength intensity readings with respect to intensity oflighting sources by correlating thermal aspects of the light source andusing an algorithm. The wavelength regions that are of particular valueinclude the ultraviolet, visible, infrared, and other spectroscopymethods such as Raman, light scattering and reflection, and fluorescencemay be used.

BACKGROUND OF THE INVENTION

Algorithms, or computer programs, have been used in improvingspectroscopic analyses for a variety of applications, some includingtemperature or thermal measurements. In U.S. Pat. No. 7,760,354, Grun,et. al. utilizes an algorithm to Raman spectroscopy to combine spectraldata. Hagler, in U.S. Pat. No. 7,426,446 uses a spectra sortingalgorithm to determine calibration training spectra for radiation.Samsoondar, in U.S. Pat. No. 6,828,152 applies algorithms of theabsorbance spectra of quality control materials. Schweitzer, et al., inU.S. Pat. No. 7,409,299 uses a ranking program with a spectral libraryto identify the composition of a sample spectra. Ingram, Jr., et. al.,in U.S. Pat. No. 7,117,132 uses an algorithm with the spectra of asurface to estimate the error statistic for a retrieved temperature of asurface material. Ja, et al., in U.S. Pat. No. 7,435,944 uses analgorithm to calculate pressure by measuring the temperature near anoptically resonant material during application of a know amount oflight. Servaites, et al. in U.S. Pat. No. 6,914,246 describes a methodand apparatus to resolve the temperatures profile of flames usingultraviolet light using an algorithm based upon a relationship between atemperature-dependent intensity range within the temperature-dependentwavelength region over a plurality of temperatures. Servaites normalizethe intensity range for a given wavelength region and was able tocalculate the thermal profile of the flames. Maynard, et al. in U.S.Pat. No. 6,654,125 utilizes current control, temperature control and analgorithm for correcting wave number drift for a laser light source andinterferometry. The algorithm is derived from spectroscopic analysis ofa reference sample with known spectrum and comparing the generatedspectrum to the known spectrum. U.S. Pat. Nos. 6,969,619, 6,830,939 and6,238,937 describe algorithms that determine the endpoint of asemiconductor processes by monitoring the spectra of the radiation.Johnson, et al. in U.S. Pat. No. 6,116,779 demonstrates an opticalmethod for measuring the temperature of thin film materials such asGallium Arsenide and Indium Phosphide that have temperature dependentband edges. Thundat, et al. uses an algorithm in U.S. Pat. No. 6,050,722to determine the temperature of a targeted sample using a non-contactinfrared temperature measuring system and micro-mechanical sensors toobtain spectra.

Cok (U.S. Pat. No. 7,158,106) deals with controlling the current inputto organic light emitting diodes (OLEDS) or LEDs by measuring thetemperature of transistor circuits.

Another Cok patent (U.S. Pat. No. 7,847,764) describes an LEDcompensation method that measures light output and an algorithm. In athird patent (U.S. Pat. No. 8,013,814) Cok describes a method for adisplay with OLEDs that deal with input signals to provide a moreuniform light output. Algorithms and input signals are used to controllight output in Cok's works.

Coates' work (U.S. Pat. Nos. 7,907,282; 7,459,713; 7,057,156 andEP1955033(A2)) describe an instrument that uses an integrated spectralsensing engine which uses software to overlap LED signals and generatespectral readings from a range of 200 nm to 25 um. This invention isintegrated into this application.

Thus, algorithms are commonly used in spectral and thermal applications,but not for measuring the light source. Often, the temperature of asample is measured for temperature and related to the generated spectra.Other applications include controlling a process by monitoring thetemperature of a radiation source with time. Still another applicationis to use electronic input variables combined with algorithms to providea more uniform light output. In all the applications the focus is oncontrolling and limiting the light or radiation source, rather than notcontrolling the light source.

For a general background, common methods of spectral analysis use asystem consisting of a light or radiant energy source (e.g., tungstenlamp), a wavelength selector or filter (e.g., a prism, monochromator toproduce light with limited and defined wavelengths), a detector orsensor, signal processor and data storage and display unit. The commonmethods are described in various instrumental analysis books that arereferenced herein.

In one method, light waves from the source are broken into specificwavelengths prior to impingement onto or through the sample of interest;this is common for absorption and Raman spectroscopy. In absorptionspectroscopy, the transmission of radiation is actually measured and theabsorbance calculated using equations 1 and 2:

T=I _(o) /I   Equation 1:

A=−log₁₀ T=log (I _(o) /I)   Equation 2:

Where:

I_(o) is the intensity of the incident light beam

I is the intensity of the light beam attenuated by the sample

T is the transmittance of the sample, is the fraction of incident lighttransmitted by the sample

A is the absorbance of the sample

A schematic of key components of an “absorption-type” instrument isshown in FIG. 1.

In another method, the light source initially passes through or isreflected from a sample prior to a wavelength selector and the detectorand signal processor and data storage and display; which are common forscattering spectroscopy, color spectrophometers and opticaldensitometers. The distinction between the absorption andscattering-type instruments is the order of the sample chamber andwavelength selectors. For the “scattering-type” instruments, the lightwaves are reflected from a solid surface or powder, and then interactwith a sensor which measures the amount of light intensity transmitted.The measured intensity is then related back to the initial intensity oflight that was produced over a wavelength or wavelength range. Thecorrected-measured intensities are then compiled, resulting in aspectrum. A schematic of key components of a scattering-type instrumentis shown in FIG. 2.

Recently a new instrument has been developed that has component order ofa scattering-type instrument, but with the light source transmittingthrough the sample, reflecting off a back surface, reflecting throughthe sample again and onto the wavelength selector. This manner uses a“transmission”-type instrument with a schematic in FIG. 3.

A special method of spectral analysis involves fluorescence,luminescence or phosphorescence, where the initial wavelength(excitation wavelength) differs from the sensing wavelength (emissionwavelength). In this case there may be separate wavelength selectorsbefore and after the sample. A schematic of the “fluorescent”-typeinstrument is shown in FIG. 4.

The spectral system has radiation or light sources that vary bywavelengths of energy. Further, the source of radiation should notchange dramatically among adjacent wavelengths. In the ultravioletrange, defined as ˜160 nm to ˜400 nm in wavelength, hydrogen ordeuterium lamps are used to yield a continuous spectrum. Typically awarm-up time of fifteen minutes is needed to stabilize the intensity ofa hydrogen or deuterium lamp.

Light waves for the visible and infrared regions are generated bytungsten, tungsten alloy, or tungsten/halogen lamps. The tungsten lampshave operating temperatures about 2870° K, and require constant voltageregulators, as the filament temperature varies greatly with inputvoltage. Tungsten lamps emit radiation from 320 nm to 2500 nm. Xenon arclamps yield radiation from 250 nm to 600 nm in wavelength. Xenon arclamps can commonly be controlled for a more uniform temperature byregular discharging from a capacitor.

Infrared light sources typically are heated electrically to temperaturesfrom 1500-2000° K. Nerst glower lamps, composed of rare earth oxides,are often used for infrared spectroscopy. The issue with the Nerst lampis that it has a large temperature coefficient of electrical resistance,and thus be heated externally to maintain a constant temperature. Asilicon carbide source, termed “globar”, may also be used for yieldinginfrared energy. The globar is electrically heated and water cooled tomaintain a more constant temperature and intensity. An incandescent wiresource, also used in the infrared region, is typically a nickel-chromiumor rhodium wire is heated by applying a current. Current regulators areneeded to maintain a more uniform temperature, and thus intensity.

Other light sources include metal vapor lamps, such as mercury andsodium vapor lamps. The vapor lamps works by applying an electricalpotential across electrodes contain the gaseous element. Initial heatingis needed to initial produce metal vapor, and then temperature of thelamp is maintained by applying a constant current. Raman spectroscopycommonly uses mercury arc lamps, and potentially could use helium,cadmium, or argon lamps. Hollow cathode lamps may be used for atomicabsorption or atomic fluorescence spectroscopy, and commonly consist ofa tungsten anode and a metal cathode in a low pressure neon or argonenvironment. The metal cathode is of the same element being analyzed. Apotential is applied to the lamp causing the metal to form an atomiccloud in a sputtering process. High electrical potentials lead to highcurrents and greater light intensities, thus a means to regulate theelectrical potential is often employed to create a more uniformintensity.

Klystrons, tunnel diodes and laser assisted plasma (LAMP) light sourcesmay be used for microwave spectra. Other light sources that may be usedfor a variety of wavelengths include lasers, LEDs (light emittingdiodes), and flames. The light sources also need electrical regulationfor an output of uniform radiation intensity. Further, the listed lightsources are examples for various spectral regions and are not inclusiveof all light sources.

The spectral systems all lack in that the light sources need aninitiation or warm-up time, sometime in the order of ten to sixtyminutes, to stabilize the light intensity. An explanation is that theelement, electrode or energy generating materials of the lamp needs athermal equilibration time, as electrons flow from a power source. Asecond equilibration is needed as the energy generating materials needto stabilize in their environment. A third equilibration occurs as thepower to the energy generating materials may vary. In summary, multiplethermal equilibriums are occurring, sometimes simultaneously, causingthe resulting light intensity to vary. When the light intensity varies,the spectra or wavelength intensity measurement of a sample will alsovary. Thus a need exists to stabilize the light intensity by way ofregulating the temperature of the energy generating material(s) or tounderstands the effect of the temperature and relate that to theintensity and spectra.

One way to improve the light intensity for an instrument is to use avery precise voltage regulator. Such a device will diminish, but nottotally remove, fluctuations in light intensity. However, even with avoltage regulator, the voltage still varies in power causing intensityfluctuations.

Another way to deal with intensity fluctuations is to use a “dual-beam”instrument that sends light through a sample and a standard. Two methodsexist for a dual beam instrument. The first is to split the light beam,using a beam splitter or prism, or mirrors, such that it passes throughboth the sample and a standard. The hope is that the light intensitiesof the two beams are exactly the same upon splitting and going throughtwo different chambers. The second method is to use a chopper-motor or“beam-chopper” to direct the light to the sample and standardintermittently. The error in intensities may be due to the appliedelectrical potential variations with time. Another issue with aninstrument is that a greater light intensities are needed since thelight will be interact with other materials and then go through both thesample and the standard to sensors. Thus, the lamp will grade at afaster rate a “single beam” instrument. If a mirror and a beam splitterapparatus is used, the instrument will require additional moving parts,thus increasing space and energy.

A dual-beam instrument is also not practical for all spectroscopicmethods, nor does it eliminate all intensity variations.

Another common method to account for lamp degradation is a “single beam”instrument. The single beam instrument uses one measurement chamber, anda standard is measured prior to measuring the sample. Then spectrum ofthe standard is subtracted from that of the sample to create a “true”spectrum. One major issue with a single-beam instrument is that thelight intensities between the sample and the standard may not be thesame, so that the “true” sample spectra may not be accurate. The singlebeam instrument lacks in that the light intensity may change orfluctuate between measurements. Additionally, the multiple measurementsemploy more resources and time.

The lifetime of a light or energy source may be correlated to theability of the sensor to detect. At the end of life phase, the lightsource has a weaker intensity compared to its starting point, causingfluctuation in intensity errors to increase. Often, this is described asa signal to noise ratio, whereby a strong signal (light intensity) ispreferred to the noise or error in detection. At the end of the usefullife of a lamp the light intensity diminishes so that the noisesignificantly affects the error in intensity, and therefore theresulting spectrum.

So, a problem exists for spectrophotometers and sensors, including thosethat measure in the ultraviolet, visible, infrared, and microwaveregions including Raman, atomic absorption and fluorescencespectroscopy, and colorimeter and densitometer instruments, in thatlight source fluctuates in intensity and changes in intensity, resultingin inaccuracies or fluctuations in resulting measurements and spectra.

Further, these light sources often need high intensities to performwell, since the light may be filtered through a prism or colored filter,and reflect off of mirrored and other surfaces, as well as through orreflected from the object of interest. Light sources also inherentlygenerate heat, and thus need a cooling apparatus or fan to dissipatesuch heat, which also may affect the light intensity due to anadditional thermal equilibrium.

Thus, a need exists for a rapid, but accurate and reproducible methodfor producing more accurate spectra or wavelength intensity readingsthat can overcome thermal and other issues associated with variablelight wave intensities.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a method for providing amore uniform spectrum or wavelength intensity output in a spectralmeasuring or sensing device that overcomes the disadvantages describedabove, in accordance with the methods described herein:

It is another object of the invention to provide a means to measure thetemperature of or near a light source and correlate said measurement tothe resultant spectra or wavelength intensity of a sample, which is dueto the intensity of the light source.

It is a further object of the invention to provide an algorithm thatperforms the function of normalizing spectra or wavelength intensity tospectra or wavelength intensity at a fixed temperature, thus obtaining amore accurate spectra or wavelength intensity compared to current onesthat vary due to thermal or other intensity effects.

Of particular significance, the invention is also directed generally tobe used for ultraviolet, visible, infrared and microwavespectrophotometers for analyzing chemical quantity and composition inaccordance with the particular instrument. Other spectroscopic methodsthat can utilize the invention include, but are not limited to, Ramanspectroscopy, light scattering and nepholometric means, fluorescence,luminescence, phosphorescence, optical densitometry, atomic absorption,atomic fluorescence, and colorimetric techniques.

Other aspects and features of the present invention will become apparentto those ordinarily skilled in the art upon review of the followingdescription of specific embodiments of the invention in conjunction withthe accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way ofexample only, with reference to the attached Figures, wherein:

FIG. 1 is a schematic of an “absorption”-type instrument for use inconjunction with the present invention.

FIG. 2 is a schematic of a “scattering”-type instrument for use inconjunction with the present invention.

FIG. 3 is a schematic of a “transmission”-type instrument for use inconjunction with the present invention.

FIG. 4 is a schematic of a “fluorescent”-type instrument for use inconjunction with the present invention.

FIG. 5 a graph of absorption spectra as a function of light sourcetemperature for a red color coding label in conjunction with the presentinvention.

FIG. 6 is a graph of absorbance at 417 nm, 475 nm, and 536 nm as afunction of light source temperature for the red color coding label inconjunction with the present invention.

FIG. 7 is a graph for comparison of absorption spectra normalizedspectrum at 25° C. for the red color coding label, with spectra measuredat 17.31° C. and 29.31° C. in conjunction with the present invention.

FIG. 8 is a graph of the L* values of a function of light sourcetemperature for the red color coding label in conjunction with thepresent invention.

FIG. 9 is graph of the a* values of a function of light sourcetemperature for the red color coding label in conjunction with thepresent invention.

FIG. 10 is a graph of the b* values of a function of light sourcetemperature for the red color coding label in conjunction with thepresent invention.

FIG. 11 is graph absorption spectra as a function of light sourcetemperature for the yellow color coding label in conjunction with thepresent invention.

FIG. 12 is a comparison of the absorption spectra normalized spectrum at25° C. for a yellow color coding label, with spectra measured at 15.50°C. and 31.69° C. in conjunction with the present invention.

FIG. 13 is a graph of absorption spectra as a function of light sourcetemperature for a blue color coding label in conjunction with thepresent invention.

FIG. 14 is a graph for comparison of the absorption spectra normalizedspectrum at 25° C. for the yellow color coding label, with spectrameasured at 15.36° C. and 30.75° C. in conjunction with the presentinvention.

DETAILED DESCRIPTION

Reference will be made to examples of the present invention.

EXAMPLE 1

A spectrophotometer (i-Lab® Model S560 with surface reader adapter) wasinitially calibrated with a white Teflon and carbon-based blackstandards. The goal was to then measure the visible spectra (400 nm to700 nm) of a red Avery® 5472™ color coding label while the temperatureof the light source varied.

In the study, two stickers were affixed to the bottom of a white Tefloncalibrator well. A tubular surface reader adapter on the instrument wasthen placed into the well. The well was then taped onto thespectrophotometer with black duct tape to ensure that its position wouldnot change. The instrument with attached calibrator was placed into athermal regulating unit (Euro Cuisine Model YM 100 Yogurt Maker) andallowed to equilibrate for one hour. The instrument with calibrator wasthen removed from the thermal regulating unit. The instrument was turnedon and the temperature of the light source (three LEDs) was measured, aswas a spectrum of the immobile, red sticker, and both recorded. Thetemperature of the light source was measured with an integrated circuittemperature sensor (Microchip TCN75A) with an accuracy of 0.0625° C.over a range from −55° C. to 125° C., that was soldered at a distance ofapproximately 6 mm from the light source. More spectral readings of thelabel were taken, as was light source temperatures. The light sourceincreased in temperature due to usage and environmental conditions. Avisible spectra of the red label as a function of temperature is shownin FIG. 5.

Note that the general effect is that as the temperature of the lightsource increases, the Absorbance intensity also increases. This isespecially evident near the 550 nm area, and most especially between the400 nm and 500 nm region. Note also that above −620 the Absorbance isnegative relative to the initial black standard.

EXAMPLE 2

The spectra of EXAMPLE 1 were processed at each wavelength using analgorithm such that a theoretical, normalized spectrum was generatedusing 25° C. as the reference temperature. FIG. 6 shows the Absorbanceof three wavelengths (417 nm, 475 nm, and 536 nm) as a function oftemperature from −17° C. to −30° C. that was part of the algorithm. FIG.6 shows that there is a linear dependency of Absorbance on light sourcetemperature, although the linearity varies at each wavelength. Thevariance may be attributed to light source differences in intensitiessince there were three LEDs used, and also absorbance characteristics ofthe sample. FIG. 7 shows the normalized spectrum from 400 nm to 700 nmusing 25° C. as the calculated standard, along with two measured spectraat light source temperatures of 17.31° C. and 29.31 ° C., forcomparative purposes. Thus, this example shows that there is arelationship between the temperature of a light source or sources andthe resulting spectrum of a sample, in this case a red color codinglabel, and that by use of an algorithm a normalized spectrum can begenerated for a specific temperature, in this case 25° C.

EXAMPLE 3

The spectra of EXAMPLE 1 was used to determine the InternationalCommission on Illumination (CIE) L*, a*, b* color values. The threevalues taken together can define a specific color; where L* islightness, with L*=0 being an all-absorbing black and L*=100 anall-reflecting white; a* is the degree of magenta to green, withnegative values being green in color and positive values being magenta;and b* is the degree of yellow to blue, with negative values being bluein color and positive values being yellow. The L*, a*, b* valuesindicate color as observed by the human eye and are calculated fromweighted absorbance at various wavelengths.

The spectral data of EXAMPLE 1 was to calculate L*, a* and b* values.FIGS. 8-10 show, respectively, the L*, a* and b* values of the redsample as a function of light source intensity. The values may benormalized with an algorithm to calculate color values for a specifictemperature.

The algorithm was made by initially measuring the temperature of thelight source and visible spectra and then developing a linearcorrelation between the temperature and the color values. Next, thecolor values were for a standard temperature (25° C.) was calculated andthose values subtracted from the raw color values, with the resultantcorrelated to the light source temperature to obtain an equation. Thelight source temperature was put into the equation to obtain a residualfor each color value. The residual, which is a function of the lightsource temperature, was then subtracted from the raw color value toobtain a “normalized” color value. Additionally, the algorithm may bewritten by measuring a minimum of two spectra and light sourcetemperatures. The algorithm may also use non-linear equations dependingon the light source temperature correlation to the spectral or colorvalues.

Table 1 shows the measured temperature of the LEDs, along with the L*,a*, b* values before (raw) and after normalization at 25° C. Inparticular, these are the L*, a*, and b* Color Values (Raw andNormalized) with Temperature of Light Source for the Red Avery® 5472™Color Coding Label.

TABLE 1 L* a* b* Temperature Normal- Normal- Normal- (Deg C.) Raw izedRaw ized Raw ized 17.31 62.2 61.0 56.4 55.4 36.0 41.9 19.25 61.9 61.056.2 55.4 37.0 41.4 21.38 61.5 61.0 55.9 55.4 38.6 41.3 23.32 61.3 61.055.7 55.4 40.0 41.3 25.50 60.9 61.0 55.4 55.4 41.7 41.4 27.06 60.7 61.055.2 55.4 42.9 41.3 28.25 60.5 61.0 55.0 55.4 44.1 41.7 29.31 60.3 61.054.9 55.4 45.0 41.7 Average 61.2 61.0 55.6 55.4 40.7 41.5 Std Dev 0.70.0 0.5 0.0 3.3 0.2

Also included are the average color values and standard deviation inmeasurements over the temperature range. Note the vast improvement inthe uniformity of color values before and after an algorithm is appliedthat accounts for the temperature of the light source. The improvementis evidenced by the marked decrease in measurement standard deviations.In summary, the values show correlations between light sourcetemperatures and color values, and that an algorithm may be furtherutilized to normalize calculated spectral values, such as color valuesfor a standard temperature.

EXAMPLE 4

The set-up and procedures of EXAMPLE 1 were followed to measure visiblespectra (400 nm to 700 nm) while the temperature of the light sourcevaried, except that the sample was now a yellow Avery® 5472™ colorcoding label.

A visible spectra of the yellow label as a function of temperature isshown in FIG. 11. Note that the general effect is that as thetemperature of the light source increases, the Absorbance intensity alsoincreases. This is especially evident between the 400 nm and 480 nmregion. Note also that above −550 nm the Absorbance is negative relativeto the initial black standard.

EXAMPLE 5

The spectra of EXAMPLE 4 were processed at each wavelength using analgorithm such that a theoretical, normalized spectrum was generatedusing 25° C. as the reference temperature. FIG. 12 shows the normalizedspectrum from 400 nm to 700 nm using 25° C. as the calculated standard,along with two measured spectra at light source temperatures of 15.50°C. and 31.69° C., for comparative purposes. Thus, this example showsthat like the red sample, there is a relationship between thetemperature of a light source or sources and the resulting spectrum of asample, in this case a yellow color coding label, and that by use of analgorithm a normalized spectrum can be generated for a specifictemperature, in this case 25° C.

EXAMPLE 6

The spectral data of EXAMPLE 4 was used to calculate L*, a* and b*values in a similar analysis manner as described in EXAMPLE 3. The rawL*, a* and b* color values were normalized with an algorithm tocalculate color values for a specific temperature. Table 2 shows themeasured temperature of the LEDs, along with the L*, a*, b* valuesbefore (raw) and after normalization at 25° C. In particular, The L*,a*, and b* Color Values (Raw and Normalized) with Temperature of LightSource for the Yellow Avery® 5472™ Color Coding Label. Also included arethe average color values and standard deviation in measurements over thetemperature range.

TABLE 2 L* a* b* Temperature Normal- Normal- Normal- (Deg C.) Raw izedRaw ized Raw ized 15.50 92.6 91.5 8.4 7.5 92.3 100.9 18.50 92.0 91.3 8.27.6 93.8 99.6 20.69 91.9 91.4 8.1 7.6 95.3 99.2 22.63 91.6 91.3 7.8 7.696.9 99.1 24.25 91.5 91.4 7.7 7.6 98.4 99.1 26.81 91.1 91.3 7.4 7.6101.0 99.4 28.56 91.0 91.4 7.2 7.6 102.9 99.7 31.69 90.8 91.5 6.8 7.5106.7 100.7 Average 91.6 91.4 7.7 7.6 98.4 99.7 Std Dev 0.6 0.1 0.5 0.04.9 0.7

Note from Table 2 the vast improvement in the uniformity of color valuesbefore and after an algorithm is applied that accounts for thetemperature of the light source. The improvement is evidenced by themarked decrease in measurement standard deviations. In summary, thevalues show correlations between light source temperatures and colorvalues for a yellow label, and that an algorithm may be further utilizedto normalize calculated spectral values, such as color values for astandard temperature.

EXAMPLE 7

The set-up and procedures of EXAMPLE 1 were followed to measure visiblespectra (400 nm to 700 nm) while the temperature of the light sourcevaried, except that the sample was now a blue Avery® 5472™ color codinglabel.

A visible spectra of the blue label as a function of temperature isshown in FIG. 13. Note that the general effect is that as thetemperature of the light source increases, the Absorbance intensity alsoincreases. This is especially evident between the 400 nm and 500 nm, and550 nm to 675 nm regions.

EXAMPLE 8

The spectra of EXAMPLE 7 were processed at each wavelength using analgorithm such that a theoretical, normalized spectrum was generatedusing 25° C. as the reference temperature. FIG. 14 shows the normalizedspectrum from 400 nm to 700 nm using 25° C. as the calculated standard,along with two measured spectra at light source temperatures of 15.36°C. and 30.75° C., for comparative purposes. Thus, this example showsthat like the red and yellow samples, there is a relationship betweenthe temperature of a light source or sources and the resulting spectrumof a sample, in this case a blue color coding label, and that by use ofan algorithm a normalized spectrum can be generated for a specifictemperature, in this case 25° C.

EXAMPLE 9

The spectral data of EXAMPLE 7 was used to calculate L*, a* and b*values in a similar analysis manner as described in EXAMPLE 3. The rawL*, a* and b* color values were normalized with an algorithm tocalculate color values for a specific temperature. Table 3 shows themeasured temperature of the LEDs, along with the L*, a*, b* valuesbefore (raw) and after normalization at 25° C. In particular The L*, a*,and b* Color Values (Raw and Normalized) with Temperature of LightSource for the Blue Avery® 5472™ Color Coding Label.

TABLE 3 L* a* b* Temperature Normal- Normal- Normal- (Deg C.) Raw izedRaw ized Raw ized 15.36 68.0 66.8 −19.2 −22.6 −38.2 −34.1 17.94 67.866.9 −19.8 −22.3 −37.5 −34.5 24.81 66.8 66.8 −22.3 −22.4 −34.5 −34.526.00 66.7 66.8 −22.6 −22.3 −34.0 −34.4 27.00 66.6 66.8 −23.0 −22.3−33.7 −34.5 27.63 66.5 66.8 −23.2 −22.3 −33.3 −34.4 28.50 66.4 66.9−23.6 −22.4 −32.9 −34.4 29.13 66.4 66.9 −23.9 −22.4 −32.6 −34.3 30.7566.1 66.9 −24.7 −22.7 −31.6 −34.0 Average 66.8 66.8 −22.5 −22.4 −34.3−34.3 Std Dev 0.7 0.0 1.8 0.1 2.2 0.2

Also included in Table 3 above are the average color values and standarddeviation in measurements over the temperature range. Note the vastimprovement in the uniformity of color values before and after analgorithm is applied that accounts for the temperature of the lightsource. The improvement is evidenced by the marked decrease inmeasurement standard deviations. In summary, the values showcorrelations between light source temperatures and color values for ablue label, and that an algorithm may be further utilized to normalizecalculated spectral values, such as color values for a standardtemperature.

The above-described embodiments of the present invention are intended tobe examples only. Alterations, modifications and variations may beeffected to the particular embodiments by those of skill in the artwithout departing from the scope of the invention, which is definedsolely by the claims appended hereto.

What is claimed is:
 1. A method for increasing the accuracy of spectralmeasurements, said method comprising: measuring a temperature of one ormore light sources that are utilized in obtaining spectral data, by useof one or more temperature sensor; and using said light sourcetemperatures and spectra to calculate a spectrum for a specifictemperature by use of an algorithm that compensates for said lightsource temperatures.
 2. The method of claim 1, wherein the measuring ofthe temperature of one or more light sources is performed by atemperature sensor in the proximity of the light source or sources. 3.The method of claim 1, wherein the spectral measurement is for one ormore electromagnetic regions selected from the group consisting of:ultraviolet, visible, near infrared, mid-near-infrared, and microwave.4. The method of claim 1, wherein the light source is formed from one ormore of radiation source selected from the group consisting of:hydrogen, deuterium, tungsten, tungsten alloy, or tungsten/halogen,mercury, Nerst glower, silicon carbide or globar, incandescent wire,sodium mercury arc, helium, cadmium, argon, hollow cathode, cathode,laser, LED, klystrons, tunnel diodes and laser assisted plasma (LAMP),and flame.
 5. The method of claim 3, wherein the light source is formedby LEDs that generate light in one or more of the ultraviolet, visible,or infrared regions.
 6. The method of claim 3, wherein the light sourcegenerates light in the ultraviolet or visible region including aradiation source containing one or both of deuterium and hydrogen. 7.The method of claim 3, wherein the light source generates light in thevisible and infrared region including a radiation source containingtungsten or tungsten-halogen.
 8. The method of claim 1, wherein thetemperature sensor includes a device capable of temperature measurementand selected from the group consisting of: a thermocouple, a thermistor,a resistance temperature deflector (RTD), a pyrometer, a Langmuir probe,an infrared device, and a thermometer.
 9. The method of claim 1, whereinthe algorithm uses a linear or non-linear correlation of spectra,wavelength intensity, or other output intensity data and relating thedata to a specific light source temperature.
 10. The method of claim 9,wherein the algorithm is usable to obtain absorption, transmission, andlight scattering values capable of further relation to concentrationand/or identification of materials.
 11. The method of claim 9, whereinthe algorithm is usable to obtain color values, including but notlimited to, L*, a*, and b*.
 12. The method of claim 1, wherein themethod is utilized in an instrument comprised of one or more LEDs assaid light source and a linear variable filter and sensor.
 13. Themethod of claim 12, wherein the spectral region utilized is theultraviolet, visible, and infrared range or combinations thereof. 14.The method of claim 12, wherein the instrument is a sensing device. 15.The method of claim 12, wherein multiple instruments may further becalibrated with each other to provide uniform results.